What does pitchstone mean?
Pitchstone is a glassy volcanic rock created when silica-rich lava cools so quickly that crystals do not have time to form. Its texture is smooth, hard, and often dark, giving it a resemblance to pitch, the tar-like material historically used for waterproofing. In geological usage, pitchstone is a broad category of volcanic glass and may be associated with rhyolitic or other felsic lava. It is sometimes confused with obsidian, but obsidian is a more specific type of naturally dark volcanic glass. Pitchstone can also preserve distinctive textures and fracture patterns that help geologists identify the rock and understand its formation.
nounPitchstone is a dark, glassy volcanic rock formed when silica-rich lava cools rapidly. It is a variety of volcanic glass and can occur in rhyolite or other felsic volcanic formations.
- A glassy volcanic rock formed by the rapid cooling of silica-rich lava.
"The cliff exposes layers of black pitchstone formed by rapidly cooled volcanic lava."
"The museum displays a polished specimen of pitchstone from a volcanic region."
"Ancient tools were made from sharp fragments of obsidian and other volcanic glasses such as pitchstone."
The plural is used when referring to multiple specimens or occurrences of the rock.
"The collection includes pitchstones from several volcanic regions."
Pitchstone gets its name from the resemblance of its dark, glassy surface to pitch, the sticky substance used to waterproof roofs and ships.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does pitchstone come from?
The word is a compound of pitch and stone. Pitch comes through Middle English from Old English pic, referring to a sticky or tar-like substance, while stone comes through Old English from Latin stana, meaning stone. The compound became established in English as a descriptive name for a dark, resin-like volcanic glass.
How pitchstone is actually used
The term is primarily used in geology and archaeology. It is less specific than obsidian, which usually refers to naturally black volcanic glass.
Easily confused with pitchstone
Pitchstone is a general term for glassy volcanic rock, whereas obsidian is a specific dark volcanic glass usually formed from silica-rich rhyolitic lava.